JPH0974249A - Semiconductor light-emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to prevent the deterioration of a semiconductor light-emitting device due to a crystal defect by a method wherein at least one interface, which comes into contact with the luminous layer, is provided with a conductive oxide layer, which can inject carriers into the light emitting layer and confine or extract light. SOLUTION: A buffer layer 12, a clad layer 13, an active layer 14 and an optical waveguide layer 5 are formed in order on a substrate 11. An insulating film 16 having a small window and an electrode layer 17, which is also used in combination as an ITO clad layer, are formed in order on the layer 15. Here, the layers 14 and 15 correspond to the first formed luminous layer. In such a way, a semiconductor light-emitting device is provided with the layer 17, which is also used in combination as the ITO clad layer, in an interface which comes into contact with the layer 15, so that the layer 17 a injects carriers into the layer 15 via a tunnel current to extract a good generated light as the layer 15 is transparent to blue light. Thereby, the tunnel current easily flows and heat is hardly generated in the junction surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device using a wide gap semiconductor, and more particularly to a semiconductor light emitting device capable of preventing deterioration due to crystal defects.

[0002]

2. Description of the Related Art Conventionally, semiconductor lasers and light emitting diodes (LEDs) made of various compound semiconductors have been widely used. However, among the semiconductor lasers and LEDs of this type, what has been put into practical use is the wavelength range from the red visible region to the infrared region in the semiconductor laser, and the light intensity LED
Then, it is the wavelength region of the semiconductor laser and the pure blue region.

In recent years, CdZnMgSSe system and InGaA have been used as light emitting device materials for short wavelength regions such as blue and green.
The 1N system has been attracting attention, and it is expected that the realization of such a semiconductor light emitting device in the short wavelength region will increase the optical density of an optical disc and the full-color outdoor message board. However, CdZnMgSSe-based and InGaAlN-based materials having a poor crystallinity and a layered structure satisfying a laser have not yet been developed. This is CdZnMgSS
In a light emitting device using an e-based or InGaAlN-based light emitting device, it is difficult to perform lattice matching of a laminated structure for light emission, and it is difficult to perform lattice matching with a heterogeneous substrate. Therefore, the device is easily deteriorated due to the occurrence of defects. , Because reliability is not ensured.
Further, in the case of the InGaAlN-based material, an LED as a blue light emitting element has been put into practical use, but not all of the visible light region is covered. Further, as a semiconductor laser, InG
In the case of aAlN system, since the sapphire substrate is used, it is difficult to form the emission surface by cleavage, and there is no report of laser oscillation yet.

On the other hand, a GaInAlP-based red light emitting device on a GaAs substrate and an In on a InP substrate which have been put to practical use.
In the case of a GaAsP-based infrared light-emitting element, a lattice structure between a laminated structure for light emission and a substrate is easy, and further, an end face is easily formed by cleavage, so that a long-life semiconductor laser and LED are achieved. . However, due to problems peculiar to materials, it is difficult to realize a light emitting device in the short wavelength region with these systems.

[0005]

As described above, the semiconductor light emitting device in the short wavelength region has various demands, but it is difficult to perform lattice matching due to the material and is reliable due to the occurrence of defects. Since it is not secured, it has not been put to practical use. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a semiconductor light emitting device capable of preventing deterioration due to crystal defects and ensuring reliability.

[0006]

The invention according to claim 1 is a semiconductor light emitting device comprising a light emitting layer formed of a compound semiconductor, wherein at least one interface in contact with the light emitting layer is the A semiconductor light emitting device comprising a conductive oxide capable of injecting carriers into a light emitting layer and confining light or extracting light. The light confinement is, for example, in the case of a conventional stripe structure laser, and it is possible to eliminate the light reflection at the electrode due to the high light confinement effect. On the other hand, light emission is taken out in the case of a surface emitting element, and since the conductive oxide is transparent to blue light, it is possible to take out light emission with high efficiency.

The invention according to claim 2 is the semiconductor light emitting device according to claim 1, wherein the interface between the light emitting layer and the conductive oxide comprises a diffraction grating. is there.

Next, the conductive oxide applied to the above semiconductor light emitting device will be described. The conductive oxide can be expected to have good carrier injection because it forms a heterostructure as a cladding material for the light emitting layer of a blue light emitting element of a wide-gap semiconductor, and its refractive index is lower than that of the light emitting layer. It is a material transparent to blue light because it can achieve good light confinement and has a large optical band gap. That is, the conductive oxide has the functions of both the conductive electrode and the cladding layer. Further, since it has the functions of the conductive electrode and the clad layer, the resistance and noise can be reduced.

As the conductive oxide of this type, for example, high-concentration tin-doped indium oxide (hereinafter referred to as ITO) or zinc oxide (ZnO) can be used. ITO has a cubic crystal structure and a lattice constant of 1.0118 nm. Therefore, ITO causes a large lattice mismatch with the material of the GaN-based or ZnSe-based blue light emitting element,
As will be described later, according to the research conducted by the present inventors, ITO is formed on p-type AlGaN used for the clad layer of the blue light emitting device.
It can be said that the material is capable of preventing the generation of heat at the junction surface and preventing the increase of crystal defects, which is a cause of element deterioration, because a tunnel current easily flows when a reverse bias is applied. The reason why the tunnel current easily flows in ITO is that the electron affinity between ITO and AlGaN is approximately equal to 4.1 to 4.3 eV and the band gap value is approximately equal. It should be noted that as the Al composition of AlGaN is increased, the electron affinity becomes smaller and the effect becomes worse. Further, when ZnSe having an electron affinity of 4.09 eV is used instead of AlGaN, a tunnel current easily flows in the same manner as described above, so that it can be applied as a modification.

Therefore, in the invention corresponding to claim 1, by taking the above means, at least one interface in contact with the light emitting layer is provided with a conductive oxide, and the conductive oxide is applied to the light emitting layer. Since carrier injection is performed and light confinement or emission extraction is performed, deterioration due to crystal defects can be prevented and reliability can be ensured.

Further, in the invention according to claim 2, since the diffraction grating is provided at the interface between the light emitting layer and the conductive oxide corresponding to claim 1, in addition to the action corresponding to claim 1,
Laser oscillation can be obtained.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a structure of a light emitting diode according to a first embodiment of the present invention. This light emitting diode has a thickness of 1 on a sapphire substrate 11 formed by metalorganic epitaxy (MOCVD).
AlN buffer layer 12 having a thickness of 00 nm, n having a thickness of 0.5 μm
Type Al _0.1 Ga _0.9 N cladding layer 13, 10 nm thick In _0.15 Ga _0.85 N active layer 14, 50 nm thick p-type G
The aN optical waveguide layer 15 is sequentially formed. Note that n-type Al
_The donor concentration of the _0.1 Ga _0.9 N cladding layer 13 is 2 × 10.
¹⁸ cm ⁻³ , and the In _0.15 Ga _0.85 N active layer 14 has a donor concentration of 1 × 10 ¹⁸ cm ⁻³ . p-type Al _0.1 Ga
_{The 0.9} N optical waveguide layer 15 has an acceptor concentration of 2 × 10 ¹⁸ cm
^-3 .

On the p-type Al _0.1 Ga _0.9 N optical waveguide layer 15, a SiN insulating film 16 having a 200 μmφ window and an ITO clad layer / electrode layer 17 having a thickness of 0.5 μm are sequentially formed. The ITO clad layer / electrode layer 17 has a donor concentration of 1 × 10 ¹⁹ cm ⁻³ . Next, a portion of the wafer having these multi-layer structure is removed by a hydrochloric acid-based chemical etching to expose the n-type Al _0.1 Ga _0.9 N cladding layer 13, n-side on the n-type Al _0.1 Ga _0.9 N cladding layer 13 A Ti / Au electrode 18 is formed by vapor deposition as an electrode.

A wafer having such a structure is 300 μm ×
A light emitting diode is formed by chipping to 300 μm. In addition, In _0.15 Ga _0.85 N active layer 14 and p-type Al
_{The 0.1} Ga _0.9 N optical waveguide layer 15 is formed according to claim 1 and claim 2.
It corresponds to the light emitting layer of.

Next, the operation of the light emitting diode configured as above will be described. In this light emitting diode, the energy band diagram of the equilibrium state is shown as in FIG.

Next, in the light emitting diode, IT
When a positive voltage is applied to the O clad layer / electrode 17 and a negative voltage is applied to the Ti / Au electrode 18 as the n-side electrode,
A forward bias is applied to the In _0.15 Ga _0.85 N active layer 14, and the ITO clad layer / electrode 17 and p-type Al _0.1 Ga are both applied.
_A reverse bias is applied to the interface with the _0.9 N optical waveguide layer 15.

At this time, in the light emitting diode, as shown in FIG. 3, electrons easily tunnel from the valence band of the p-type Al _0.1 Ga _0.9 N optical waveguide layer 15 to the conduction band of the ITO clad layer / electrode 17, p-type Al _0.1 Ga _0.9 N optical waveguide layer 1
Excessive holes are generated in the valence band of 5 and these holes are In
It is implanted into the _0.15 Ga _0.85 N active layer 14.

Therefore, in the In _0.15 Ga _0.85 N active layer 14, the holes and the n-type Al _0.1 Ga _0.9 N cladding layer 1 are formed.
Electrons injected into the conduction band from 3 are recombined to generate light emission.

At this time, the light emission characteristic is that the operating current is 20 mA.
The wavelength was 420 nm and the brightness was 2 candela. The operating voltage is 4V. Furthermore, under these conditions, 10
We were able to confirm the operation for over 000 hours.

As described above, according to the first embodiment, the ITO clad layer / electrode 17 is provided at the interface in contact with the p-type Al _0.1 Ga _0.9 N optical waveguide layer 15, and the ITO clad layer / electrode 17 is a tunnel. P-type Al _0.1 G via electric current
Since a carrier (hole) is injected into the a _0.9 N optical waveguide layer 15 and it is transparent to blue light, excellent emission extraction is achieved. Therefore, a tunnel current easily flows to the junction surface. Since it is difficult to generate heat, it is possible to prevent deterioration due to crystal defects even though the lattice is irregular, and it is possible to ensure reliability.

Next, a semiconductor laser according to the second embodiment of the present invention will be described. FIG. 4 is a bird's-eye view showing the structure of this semiconductor laser. This semiconductor laser has a 100 nm thick AlN buffer layer 22 formed on a sapphire substrate 21 by a metal organic epitaxy method (MOCVD).
N-type Al _0.1 Ga _0.9 N cladding layer 2 having a thickness of 0.5 μm
3. An In _0.15 Ga _0.85 N active layer 24 having a thickness of 10 nm and a p-type Al _0.1 Ga _0.9 N optical waveguide layer 25 having a thickness of 50 nm are sequentially formed. The n-type Al _0.1 Ga _0.9 N cladding layer 23 has a donor concentration of 2 × 10 ¹⁸ cm ⁻³ , and
_{The 0.15} Ga _0.85 N active layer 24 has a donor concentration of 1 × 10 ¹⁸ c.
m ^-3 . The p-type Al _0.1 Ga _0.9 N optical waveguide layer 25 has an acceptor concentration of 2 × 10 ¹⁸ cm ⁻³ .

A second-order diffraction grating 26 having a depth of 20 nm and a pitch of 150 nm is formed on the p-type Al _0.1 Ga _0.9 N optical waveguide layer 25, and a thickness of 0.5 μm is formed on the diffraction grating 26.
m of ITO clad layer / electrode layer 27 are sequentially formed.
The ITO clad layer / electrode layer 27 has a donor concentration of 1 × 10
¹⁹ cm ^-3 . Next, a stripe mask having a width of 10 μm is formed on the wafer having these multilayer structures, and a part of the wafer is removed by hydrochloric acid chemical etching through the stripe mask to remove the n-type Al _0.1 Ga _0.9 N cladding layer 23. And a Ti / Au electrode 28 is formed as an n-side electrode by vapor deposition on the n-type Al _0.1 Ga _0.9 N cladding layer 23.

A wafer having such a structure has a cavity length of 1 m.
A semiconductor laser is formed by chipping into m. next,
The operation of such a semiconductor laser will be described.

In this semiconductor laser, when a voltage is applied in the same manner as described above, when the threshold current is 50 mA, the wavelength 4
A room temperature continuous oscillation with a maximum output of 100 mW at 20 nm was obtained. Furthermore, with this semiconductor laser, the ambient temperature is 50 ° C.,
It was possible to confirm the operation for 10,000 hours or more under the condition of the light output of 30 mW.

The reason why such good characteristics are obtained is as follows.
Similarly to the above, when a forward bias is applied to the In _0.15 Ga _0.85 N active layer 24, p-type GaN is generated by the tunnel current.
Excessive holes are generated in the valence band of the optical waveguide layer 25, and these holes are injected into the In _0.15 Ga _0.85 N active layer 24, so that In
_0.15 Ga _0.85 In addition to good carrier injection effect of recombination at the N active layer 24, an In _0.15 Ga _0.85 N active layer 24 and p-type Al _0.1 Ga _0.9 N optical guide layer 25 ITO clad than the equivalent refractive index of the Because the refractive index of the layer / electrode layer 27 is considerably low, a good light confinement effect is produced.

As described above, according to the second embodiment, in addition to the good carrier injection effect similar to that of the first embodiment, In _0.15 Ga _0.85 N active layer 24 and p-type Al are formed.
The equivalent index of refraction of the _0.1 Ga _0.9 N optical waveguide layer 25 is ITO.
Since the refractive index of the clad layer / electrode layer 27 is considerably low, a good light confining effect can be obtained.

That is, according to the present embodiment, even in the semiconductor laser having the stripe structure, as in the first embodiment, the deterioration due to the crystal defects can be prevented even though the lattice is irregular. , Reliability can be secured.

Further, according to the present embodiment, p-type Al
_{Since a} diffraction grating is provided at the interface between the _0.1 Ga _0.9 N optical waveguide layer and ITO, laser oscillation can be obtained. Next, a semiconductor laser according to the third embodiment of the present invention will be described.

FIG. 5 is a sectional view showing the structure of this semiconductor laser. The same parts as those in FIG. 1 are designated by the same reference numerals and detailed description thereof will be omitted, and only different parts will be described here.

That is, the semiconductor laser according to the present embodiment is more p-type Al _0.1 Ga _0.9 N than the device shown in FIG.
A diffraction grating 31 is provided at the interface between the optical waveguide layer 15 and the ITO clad layer / electrode layer 17. The diffraction grating 31 is formed by concentric circular secondary gratings having a depth of 20 nm and a pitch of 150 nm. The other layer structure is similar to that shown in FIG. 1, and a semiconductor laser is formed by chipping into 300 μm × 300 μm.

In this semiconductor laser, the threshold value is 70 mA, the wavelength is 420 nm, and the maximum output is 200.
A room temperature continuous oscillation of mW was obtained. Furthermore, this semiconductor laser has a temperature of 50 ° C. and an optical output of 30 mW.
The operation of more than 0000 hours could be confirmed.

The reason why such good characteristics are obtained is as follows.
This is because, in addition to the good effect of carrier injection similar to that of the second embodiment, since ITO is transparent to the blue wavelength range, it is possible to extract light with high efficiency.

As described above, according to the third embodiment, in addition to the same good carrier injection effect as that of the second embodiment, the same good light extraction effect as that of the first embodiment is obtained. be able to.

That is, according to the present embodiment, even in the surface-emitting type semiconductor laser, similarly to the first embodiment, it is possible to prevent deterioration due to crystal defects despite the lattice mismatch. Therefore, reliability can be secured.

In the first to third embodiments described above, the case where ITO is used as the cladding layer of the GaN blue light emitting element has been described, but the present invention is not limited to this, and ZnS is used.
Even if ITO is used as the clad layer of the e-based blue light emitting element, the same effects can be obtained by carrying out the present invention in the same manner. This is because the junction between ITO and p-type ZnSe is GaN.
This is because the ZnSe system has an electron affinity of ITO of 4.1 to 4.3 eV, which is similar to the GaN system.
Due to being in the range of.

In the first to third embodiments, the case where ITO is used as the conductive oxide semiconductor material has been described, but the present invention is not limited to this, and ITO is used instead of ITO.
Even if zinc oxide (ZnO) is used, the present invention can be similarly carried out and the same effect can be obtained.

In the first to third embodiments described above, the case where the conductive oxide semiconductor material is formed on the GaN-based epi layer has been described. For example, a GaN-based material is formed on the ZnO buffer layer. The same effect can be obtained by forming the epi layer.

Further, in the third embodiment, the case where the diffraction grating has one pitch has been described.
Not limited to this, even if two or more kinds of pitches of diffraction gratings are provided, the present invention can be similarly implemented to obtain the same effect, and a radiation beam pattern with good symmetry of laser light can be obtained. it can. In addition, the present invention can be modified in various ways without departing from the scope of the invention.

[0039]

As described above, according to the invention of claim 1, a conductive oxide is provided on at least one interface in contact with the light emitting layer, and the conductive oxide performs carrier injection into the light emitting layer. In addition, since the light is confined or the light is extracted, it is possible to provide a semiconductor light emitting device which can prevent deterioration due to crystal defects and ensure reliability.

According to the invention of claim 2, claim 1
Since the diffraction grating is provided at the interface between the light emitting layer and the conductive oxide, the semiconductor light emitting device which can obtain laser oscillation can be provided in addition to the effect of the first aspect.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a light emitting diode according to a first embodiment of the present invention,

FIG. 2 is an energy band diagram of an equilibrium state in the same embodiment,

FIG. 3 is an energy band diagram of a bias applied state in the same embodiment,

FIG. 4 is a bird's-eye view showing the structure of a semiconductor laser according to a second embodiment of the present invention,

FIG. 5 is a sectional view showing the structure of a semiconductor laser according to a third embodiment of the present invention.

[Explanation of symbols]

11, 21 ... Sapphire substrate, 12, 22 ... AlN buffer layer, 13, 23 ... n-type Al _0.1 Ga _0.9 N cladding layer, 14, 24 ... In _0.15 Ga _0.85 N active layer, 15, 2
5 ... Al _0.1 Ga _0.9 N optical waveguide layer, 16 ... SiN insulating film, 17, 27 ... ITO clad layer / electrode layer, 18, 2
8 ... Ti / Au electrodes, 26, 31 ... Diffraction grating.

Claims (2)

[Claims] 1. A semiconductor light emitting device comprising a light emitting layer formed of a compound semiconductor, wherein at least one interface in contact with the light emitting layer is provided with carrier injection into the light emitting layer and is optically closed. A semiconductor light-emitting device comprising a conductive oxide capable of filling or emitting light. 2. The semiconductor light emitting device according to claim 1, wherein a diffraction grating is provided at an interface between the light emitting layer and the conductive oxide.